Manual preset interval timer with latch holding means for contacts

ABSTRACT

Slow or incomplete closure of manual preset interval timer contacts during the setting operation is avoided by a latch which prevents closure of the contacts until the timer knob has been turned far enough to insure complete closure of the contacts. This latch allows the contacts to assume very close proximity before releasing. This closes the contacts with a positive and rapid movement and avoids contact bounce.

United States Patent 1 1 9, 1 Harris [4 1 Oct. 17, 1972 [54] MANUAL PRESET INTERVAL TIMER 2,925,478 z/l9s6 vamasaki ..'...20o/33 B x WITH LATCH HOLDING MEANS FOR 2,960,582 11/1960 Harris ..74/54 X CONTACTS 1 3,100,823 8/1963 Wagner ..200/39 R 3,107,281 101963 T ft ..20O 39R X [721 "arris, Delafield, 1 3,199,012 8/1965 l-l rr is .200/39 R x 73 Assignee; De|tro|Corp Be|]wood, L 1 3,264,817 8/1966 Beguin ..200/38 FB X 3,599,006 3/.1971 Harris ..200/39 R X [22] Filed: Sept. 7, 1971 i Primary Examiner.l. R. Scott [57] I ABSTRACT [52] "260/38 5 32 3 Slow or incomplete closure of manual Preset interval timer contacts during the setting operation is avoided [51] Int. Cl. ..H0lh 7/08, HOlh 43/10 I by a latch which prevents closure of the contacts until [581 of Search-"mm 35 R2 35 37 l the timer knob has been turned far enough to insure 200/38 38 38 8 38 F132 38 1 complete closure of the contacts. This latch allows the 39 166 l contacts to assume-very close proximity before releas- 569 ing. This closes the contacts with a positive and rapid movement and avoids contact bounce. [56] References Cited I 7 Claims, 3 Drawing Figures UNITED STATES PATENTS 2,528,841 11/1950 Morrison et a1 ..200/37 A X PATENTED 17 3.699.281

INV EN TOR.

MANUAL PRESET INTERVAL TIMER WITH LATCH HOLDING MEANS FOR CONTACTS BACKGROUND OF THE INVENTION Manual preset interval timers common in the art include acam operated switch. The cam is on a shaft which is settable manually by a knob and which is driven to the off position by a timing mechanism. In order to save on both space and costs, the switch is of the non snap action variety. Snap actionat the off position is obtained by dropping into a notch on the cam. When the timer knob is moved manually from the off position, the timer switch recloses at a rate depending on how fast the user turns the knob. At one point in manual setting of the knob, the contacts touch but with no contact pressure. If the setting motion of the user is slow or hesitating at this critical point, the contacts can burn and even weld together. This is especially true where the timer controls high inrush loads such as infra-red lights in heating apparatus.

BRIEF SUMMARY OF INVENTION The primary object of the present invention is to provide a manual preset interval timer with a simple low cost mechanism for causing the switch contacts to close rapidly and positively when the timer is manually set.

A further object is'the provision of such an arrangement which avoids contact bounce.

In accordance with the preferred form of the invention, the switch includes a blade carrying a movable contact biased against a stationary contact. A cam follower rides a lost motion cam on the manual set shaft and is provided with a spring. When the timer times out, the follower drops into a notch in the cam and moves the blade to separate the contacts. A latch now comes in place under the blade. This latch is actuated by a second cam fixed to the shaft and which actuates the switch cam through a lost motion connection. When the user sets the knob for a timing cycle, the switch cam follower is first cammed out of the way of the switch, and then the latch is released to allow the bias of the switch blade to close the contacts. The latch is proportioned to allow the contacts to almost touch before releasing. This small gap prevents excessive velocity in contact closure and prevents contact bounce.

Other objects of the invention will appear from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a front view of a timer with the front plate removed and showing the parts in the of position.

FIG. 2 is a bottom view of FIG. 1.

FIG. 3 is a view similar to FIG. 1 but showing the parts in the position assumed just before the timer. switch closes when the timer is being set.

DETAILED DESCRIPTION OF INVENTION Referring to FIGS. 1 and 2 the timer mechanism is enclosed in a housing, generally indicated as 1. This housing includes a front plate 2, a back plate 3 and side members 4. The housing 1 at its upper end supports a switch panel 5 carrying a contact bracket 6 and a switch blade bracket 7. The bracket 7 carries an L shaped switch blade 8 carrying a movable contact 9.

The contact bracket 6 extends-downwardly beyond the end of blade 8 and carries the stationary contact 10. The blade 8 is biased downwardly tending to engage the contacts 9 and 10. This blade is actuated by a cam follower 11 which is of L shaped construction, one leg 12 being formed as a cam follower and the other leg 13 serving to engage the switch blade 8 adjacent contact 9. This cam follower is preferably molded with a shaft portion 15 which extends freely between plates 2 and 3 and which carries a torsion spring 16. One leg of the torsion spring 16 bears against a stud l7 and the other leg bears against a stud 18 formed on the cam follower. It will be apparent that spring 16 serves to bias the cam follower 11 counter-clockwise about its pivot. The biasing force of the spring 16 overcomes the bias of the switch blade 8, causing the contacts 9 and 10 to be disengaged as shown in FIG. 1.

The cam follower portion 12 of cam follower ll rides on a cam 20 which is freely mounted on a cam shaft 21 which extends between the plates 2 and 3. This cam shaft is driven by a gear 22 which-is driven by the pinion 23 of motor 24. At its other end, the cam shaft 21 carries a knob 25 which is operated by the user in manually presetting the timer. A suitable friction drive 26 is interposed between the gear-22 and shaft 21 to permit such manual rotation of the shaft with-out damaging the gearing and motor.

The cam follower portion 12 of the cam follower as shown in FIG. 1 is received in a notch 27 in cam 20 when the timer is in the OFF position. The carn shaft 21 also carries a second cam 28 which is rigidly mounted on the shaft. This second cam includes a pin 29 which extends rearwardly into a slot 30 formed in the lost motion cam 20. The pin 29 on rigid cam 28 and the slot 30 in cam 20 constitute a lost motion drive means between the cam shaft 21 and cam 20.

As shown in FIG. 1, the switch blade 8 extends beyond the moveable contact 9 and out over a latch member 32. This latch member is molded with a shaft portion 33 extending freely between the front and back plates of the housing. The latch member 32 also includes a cam follower portion 34 which rides on the rigid cam 28. As shown in FIG. 2, the latch member 32 is provided with an offset allowing it to ride the cam 28 and also to extend forwardly of thecontact bracket 6. The latch member 32 also includes an inwardly extending portion 35 which extends under the end of the switch blade 8. A torsion type biasing spring 36 is mounted over the hub portion 33. One end of this spring bears against a stud 37 molded on the cam follower 32 and the other end of this spring bears on a stud 38 attached to the housing. It will be apparent that the spring 36 serves to bias the latch 32 inwardly causing the cam follower portion 34 to ride on cam 28. Cam 28 includes a circular high portion 39 and a notch portion 40 which is arranged to lift the cam follower 34 upon rotation of the cam shaft in either direction.

OPERATION With the'parts in the positions shown in FIG. 1, the timer is in the OFF position. The cam follower portion 12 of cam follower 11 is in the notch 27 of cam 20 and the switch operator portion 13 of the cam follower has lifted the blade 8 for separating the movable contact 9 from the stationary contact 10 by a substantial distance. The cam follower portion 34 of latch 32 is in notch 40 of cam 28, causing the switch operating portion 35 to be in the path of the end of switch blade 8. In this off position of the cam shaft, the stud 29 on rigid cam 28 is engaging the right hand end of the slot 30 of the lost motion cam 20.

When the manual knob 25 is turned in a clockwise direction as seen in FIG. 1, the cam 28 rotates with the camshaft and the stud 29 engaging the right hand end of slot 30 in cam 20 causes cam 20 to be rotated clockwise along with the cam shaft. During the initial setting motion of the cam shaft, the parts assume the position shown in FIG. 3. Here the cam follower portion 12 of follower l 1 has cammed substantially all the way out of the notch 27 causing the portion 13 of the cam follower to be spaced from the switch blade 8. At this time the switch blade 8 is restrained from further downward motion by the cam follower or latch member 32 with the movable contact 9 almost engagin g the stationary contact 10. The cam follower portion 34 of latch 32 is engaging the rise portion of cam 28 connecting the low and high portions 40 and 39 of this cam.

On continued rotation of the cam shaft 21 in a clockwise direction by knob 25, the cam 28 causes rotation of latch member 32 in a counterclockwise direction. Also the cam follower portion 12 rides the top surface of cam 20. Shortly after this occurs, latch 32 releases switch blade 8 and the contact 9 drops to engagement-with contact 10 with a positive continuous movement. Due to the proximity of the contact 9 with contact 10 when the blade is released, the time for acceleration of switch blade 8 is extremely small and build up of high velocity is avoided. Thus contact 9 engages contact 10 at a relatively slow velocity and with full contact pressure which avoids contact bounce.

On continued rotation of the shaft 21 to the timing desired by the user, the cam follower 11 rides the generally circular portion 41 of cam and the cam follower portion 34 of latch 32 rides on the circular portion 41 of cam 28. Engagement of contacts 9 and 10 energizes the timer motor and load in a manner well known in the art. The timer motor now runs and it drives the camshaft 21 in a counterclockwise direction back to the Off position. Before the cam shaft reaches this position, the low portion 40 of cam 28 comes under cam follower portion 34 of the latch 32. At this time, however the inwardly extending portion 35 of latch 32 is bearing against the end of switch blade 8 and the follower 34 thus does not drop to the bottom of the notch. When the timer reaches the Off position, the follower portion 12 of cam follower 11 rides down the curved end portion of notch 27. This occurs with rapid action due to the lost motion provided by stud 29 and notch in cam 20. Cam 20 thus advances counterclockwise rapidly and the cam follower 11 drops rapidly into the notch of the cam. This action is caused by the spring 16 and this causes the cam follower 13 to lift switch blade 8 causing the movable contact 9 to be separated from the stationary contact 10 by a substantial distance. When the end of switch blade 8 clears the end of the latch 35, the spring 36 causes movement of the latch portion back under the end of switch blade 8. The parts are now ready for a new cycle of operation.

It should be noted that the opposite ends of notch 27 .in cam 20 and notch 40 in cam 28 are symmetrical.

This allows the timer to be turned in either direction from the OFF position in order to start a time cycle. Thus when the cam shaft 21 is rotated counterclockwise from the Offlposition, the cam follower portions 12 and 34 are operated in the same sequence causing the switch operator portion 13 to first clear the switch blade 8 and then causing the latch portion 35 to disengage the blade 8 to engage the contacts with rapid action.

From the foregoing it will be apparent that the present invention provides a manual preset timing mechanism which causes the contacts to engage with a rapid bounceless action irrespective of the speed at which the shaft is turned by. the operator.

Inasmuch as many modifications may be made in the embodiment disclosed without departing from the spirit and scope of the invention, it is desired to be limited only by the scope of the appended claim.

I claim:

1. In a manual preset interval timer, the combination of, a load switch comprising a relatively stationary contact and a relatively movable contact, means including cam follower means arranged to actuate the movable contact, a cam shaft having cam means arranged to actuate the cam follower means, timing means for driving the cam shaft, manual means for manually setting the cam shaft, said cam follower means and cam means being constructed and arranged to cause separation of the movable contact from the stationary contact with rapid action at a predetermined position of the cam shaft, and to cause the movable contact to engage the stationary contact when the cam shaft is away from said position, latch means movable into latching position when the contacts areseparated for holding the contacts separated, and means on the cam shaft for releasing said latch means as the cam shaft is manually moved away from said predetermined position causing the contacts to engage with rapid action independent of the speed at which the cam shaft is manually set.

2. The combination recited in claim 1 in which the movable contact is biased toward the relatively stationary contact and in which the cam follower means is biased in a direction to disengage the movable contact with sufficient force to overcome the bias of the movable contact, the cam means being generally circular and having a drop-off into which the cam follower drops at said predetermined position.

3. The combination recited in claim 1 in which the cam means and cam follower means separates the contacts with a relatively wide gap and in which the latch means allows the gap to become relatively small before releasing.

4. The combination recited in claim 1 in which the cam means and latch releasing means on the cam shaft are double acting, permitting manual rotation of the cam shaft in either direction from said predetermined position.

5. The combination recited in claim 1 in which the latch releasing means is rigidly mounted on the shaft and the cam means is mounted loosely on the shaft and driven by the latch releasing means.

6. The combination recited in claim 2 in which the cam means and latch releasing means on the cam shaft are double acting, permitting manual rotation of the cam shaft in either direction from said predetermined position.

7. The combination recited in claim 2 in which the latch releasing means is rigidly mounted on the shaft 5 and the cam means is mounted loosely on the shaft and driven by the latch releasing means. 

1. In a maNual preset interval timer, the combination of, a load switch comprising a relatively stationary contact and a relatively movable contact, means including cam follower means arranged to actuate the movable contact, a cam shaft having cam means arranged to actuate the cam follower means, timing means for driving the cam shaft, manual means for manually setting the cam shaft, said cam follower means and cam means being constructed and arranged to cause separation of the movable contact from the stationary contact with rapid action at a predetermined position of the cam shaft, and to cause the movable contact to engage the stationary contact when the cam shaft is away from said position, latch means movable into latching position when the contacts are separated for holding the contacts separated, and means on the cam shaft for releasing said latch means as the cam shaft is manually moved away from said predetermined position causing the contacts to engage with rapid action independent of the speed at which the cam shaft is manually set.
 2. The combination recited in claim 1 in which the movable contact is biased toward the relatively stationary contact and in which the cam follower means is biased in a direction to disengage the movable contact with sufficient force to overcome the bias of the movable contact, the cam means being generally circular and having a drop-off into which the cam follower drops at said predetermined position.
 3. The combination recited in claim 1 in which the cam means and cam follower means separates the contacts with a relatively wide gap and in which the latch means allows the gap to become relatively small before releasing.
 4. The combination recited in claim 1 in which the cam means and latch releasing means on the cam shaft are double acting, permitting manual rotation of the cam shaft in either direction from said predetermined position.
 5. The combination recited in claim 1 in which the latch releasing means is rigidly mounted on the shaft and the cam means is mounted loosely on the shaft and driven by the latch releasing means.
 6. The combination recited in claim 2 in which the cam means and latch releasing means on the cam shaft are double acting, permitting manual rotation of the cam shaft in either direction from said predetermined position.
 7. The combination recited in claim 2 in which the latch releasing means is rigidly mounted on the shaft and the cam means is mounted loosely on the shaft and driven by the latch releasing means. 